on a x86 system ,os 4.6 i can see user manager package in system-->packages but
there is not user manager menu in tools.
also http://router ip/username is not accessable.should i install the package?

Put the package in the root of the files system and when you reload you should be able to get to the url http://yourdevice/userman and login with admin and no password.

If you mean 'tools' in winbox, you're not going to find it there. You can only configure it by CLI:
hit 'New terminal' from the menu list on the left and in the terminal window type 'tool userman' - it's all in the wiki (wiki.mikrotik.com).
To check out userman 4, be sure to install the test version http://mikrotik.com/download/userman-test-4.6.npk
http://routerip/username will not be accessible until you've properly setup userman; again check out the wiki.

Problem solved,thank you.